User input interfaces are used in many different types of electronic devices and generally allow human users to enter data and/or commands into an electronic format. A keypad is a type of user input interface in which one or more keys or buttons are used to enter the data and/or commands. In some keypads, the keys are movably mounted such that application of a force to a key causes the key to move relative to another portion of the keypad. Movement of the key can then be sensed electrically, for example, by causing electrical continuity to occur within a circuit. The force that moves the keys on a keypad is typically provided by the human user's finger. In other types of keypads, the keys may be stationary and user input may be sensed using, for example, either resistive or capacitive sensing technologies.
Keypads are used in many other applications, in addition to mobile telephone devices. Examples of such other applications that typically utilize keypads include electronic dictionaries, personal digital assistants (PDAs), handheld game consoles, security input pads for allowing selective entry into a facility or area and remote control devices for video and audio appliances.
A keypad may include multiple keys, each corresponding to a different command and/or data input selection. An example of a keypad with multiple keys is the type of keypad commonly used in mobile telephone devices. In a mobile telephone device, the keypad may, for example, include individual keys for each of the digits 0 through 9 to allow telephone numbers to be entered into the mobile telephone device. To help a human user interface with an electronic device via a keypad, the keys on a keypad typically include icons to identify what command or data input selection each key represents. In the example of a mobile telephone device keypad, as discussed above, the keys for each of the digits 0 through 9 may each include an appropriate icon indicating the digit that each key represents (the key that corresponds to 0 would include the icon “0”, and so on). Keys often may serve different functions or data input selections when, for example, the device is in different modes of operation.
In order to facilitate use of a keypad in low ambient light situations, many keypads include a backlighting feature in which one or more light sources illuminates the keys from beneath. This backlighting generally causes each key to be lighted so that it can readily be found and identified.
To enhance optimum usability of keypad devices in low ambient light situations, it is desirable to provide keyboard backlighting that is both sufficient in intensity and relatively uniform in distribution across the illuminated keys.